The effect of acute branched-chain amino acid supplementation on prolonged exercise capacity in a warm environment

Eight males were recruited to examine the effect of branched-chain amino acid (BCAA) supplementation on exercise capacity in a glycogen-depleted state in a warm environment. Following a exercise and dietary regimen designed to reduce glycogen availability, subjects returned to the laboratory the following morning and remained seated for 2 h, before cycling to volitional exhaustion at 50% O₂ peak in a warm environment [30.0 (0.2)°C; mean (SD)]. Four 250 ml aliquots of a 12 g l^–1 BCAA solution or placebo were ingested at 30 min intervals prior to exercise, with an additional 150 ml consumed every 15 min throughout exercise. BCAA ingestion had no effect on exercise capacity [placebo 103.9 (26.9) min; BCAA 111.0 (29.2) min; P=0.129). No difference in heart rate (P=0.345), core temperature (P=0.628), or weighted mean skin temperature (P=0.114) was apparent between trials. Ingestion of the BCAA solution produced a marked increase in plasma BCAA immediately prior to exercise [+1126 (158) mol l^–1; P<0.001) with this difference maintained throughout. Consequently, a significant reduction in the plasma concentration ratio of free tryptophan to BCAA was observed during the BCAA trial when compared to the placebo (P<0.001). Plasma ammonia concentration was significantly elevated during exercise throughout the BCAA trial (P<0.001), with no change from rest apparent during the placebo trial (P=0.608). Blood glucose (P=0.114) and lactate (P=0.836) concentrations were not different between trials. Ingestion of a BCAA solution prior to, and during, prolonged exercise in glycogen-depleted subjects did not influence exercise capacity in a warm environment.     

Entry into hibernation in M. Flaviventris: Sleep and behavioral thermoregulation

Hibernators of the genus Marmota (wt=3–5 kg) differ from smaller hibernators (wt<1 kg) in thermoregulatory characteristics during entry into hibernation. They might be expected to differ also with respect to the distributions of activity, awake and sleep states during entry. Marmots implanted stereotaxically with electrodes to record electroencephalograms and brain temperature (T_Br) were monitored remotely by a polygraph as well as video transmission as they entered hibernation. During entry, awake (A), slow wave sleep (SWS), and paradoxical sleep (PS) states could be identified. Activity which included nest building, grooming, and shivering slowed entry and became progressively more stereotyped as T_Br decreased. All animals exhibited at least one PS bout between T_Br=33?32°C. SWS as percent of total sleep increased (80 to 92%) as T_Br decreased from 35?25°C. This increase represented a decrease in number and increase in duration of SWS episodes. The length of individual SWS and PS episodes of the marmot did not differ from those reported in Citellus. These data suggest that entry into hibernation is a more complex phenomenon than merely an extension of slow wave sleep. Similar changes in arousal state distribution occur in hibernators of different sizes.     

A narrative review of thermoregulation techniques used by paediatric theatre staff during intra hospital transfer from paediatric theatres to the Neonatal Intensive Care Unit ( NICU)

IntroductionEffective thermoregulatory care during neonatal transfer for surgical procedures is crucial in preventing inadvertent neonatal hypothermia. This narrative review thereby aims to investigate thermoregulation techniques used by paediatric theatre staff to prevent neonatal hypothermia during the neonate's surgical journey from theatres to Neonatal Intensive Care Unit (NICU).Key findingsThe review highlights the importance of continual temperature monitoring in ensuring prevention and diagnosis of hypothermia during intra hospital transfer. Additionally considerations for prevention of hypothermia in the theatre setting are identified including pre warming the theatre environment and equipment. The literature also identified that during intra hospital transfer of neonates following surgery there is a lack of specific guidelines relating to the exact combination of thermoregulation techniques required during such transfers. To prevent practices which are guided by theatre staff preference, findings suggest that guidelines are implemented that are clear, specific and standardised within surgical neonatal intra hospital transfer.ConclusionsThere is a lack of clinical guidelines pertaining specifically towards neonatal intra hospital transfer following neonatal surgery. Consequently, neonatal hypothermia has been reported post-transfer in research and the practice setting following transfers between Theatres to NICU. Thereby, further investigation of paediatric theatre staff neonatal thermoregulatory care is required along with the introduction of national standardised guidelines and paediatric theatre staff education to ensure evidence based practice.     

Computer Simulation of Heat Transfer in Different Tissue Layers of Body Extremities Under Heat Stress in Deep Anesthetic Condition

Many mathematical models of thermoregulation in humans have been developed, so far. These models appeared to be very useful tools for studying temperature regulation in humans under adverse environmental conditions. However, no one discussed the heat transfer characteristics of denervated subjects. Thus, the present study is concerned with aspects of the passive system for denervated subjects: (1) modeling the human body extremities (2) modeling heat transport mechanism within the body and at its periphery. The present model was simulated using the software (Wintherm 8.0, Thermoanalytics, USA) for different body segments to predict the heat flow between body core and skin surface with changes in environmental temperature with fixed relative humidity and wind velocity. The simulated model for comparative study of internal temperature distribution of hand, arm, leg and feet segments yielded remarkably good results and observed to be in trends with previously cited work under ambient environmental condition and at controlled room temperature. Models could be used to measure the temperature distribution in human limbs during local hyperthermia and to investigate the interaction between limbs and the thermal environment.     

通过激活TRPV1达到快速有效治疗性浅低温方法的探讨

目的:通过二氢辣椒碱(DHC)调控瞬时受体电位阳离子通道香草酸亚型1(TRPV1),探讨达到治疗性浅低温的方法。方法:(1)观察不同剂量DHC(2、3和4 mg/kg)皮下注射对小鼠体温的影响,以20%DMSO溶于生理盐水为对照组,寻求达到目标温度(32~34℃)所需的最佳剂量;(2)清醒CD-1小鼠单次皮下注射最佳剂量DHC后,按1 mg·kg-1·h-1的速度持续输注DHC,观察是否有快速降温及维持治疗性浅低温的最长时间;(3)相同剂量DHC皮下注射于成年(9~10周)和老年(24~27月)小鼠,观察小鼠体温变化。结果:(1)单次注射2mg/kg DHC可在15 min内达到治疗性浅低温;(2)单次注射2 mg/kg DHC后,按1 mg·kg-1·h-1的速度持续输注DHC可快速降温,还可维持治疗性浅低温6 h;(3)DHC介导的低体温在不同年龄模型中均适用。结论:DHC通过激活TRPV1通路可产生治疗性低体温,该方法可达到更强和更久的中心体温降低,在不同年龄模型中均适用。     

Methamphetamine-induced toxicity: An updated review on issues related to hyperthermia

Reports of methamphetamine-related emergency room visits suggest that elevated body temperature is a universal presenting symptom, with lethal overdoses generally associated with extreme hyperthermia. This review summarizes the available information on methamphetamine toxicity as it pertains to elevations in body temperature. First, a brief overview of thermoregulatory mechanisms is presented. Next, central and peripheral targets that have been considered for potential involvement in methamphetamine hyperthermia are discussed. Finally, future areas of investigation are proposed, as further studies are needed to provide greater insight into the mechanisms that mediate the alterations in body temperature elicited by methamphetamine.     

Local differences in sweat secretion from the head during rest and exercise in the heat

The importance of the head in dissipating body heat under hot conditions is well recognised, although very little is known about local differences in sweat secretion across the surface of the head. In this study, we focused on the intra-segmental distribution of head sweating. Ten healthy males were exposed to passive heating and exercise-induced hyperthermia (36 degrees C, 60% relative humidity, water-perfusion suit: 46 degrees C), with ventilated sweat capsules (3.16 cm(2)) used to measure sweat rates from the forehead and nine sites inside the hairline. Sweat secretion from both non-hairy (glabrous) and hairy areas of the head increased linearly with increments in work rate and core temperature, with heart rate and core temperature peaking at 175 b min(-1) (+/-6) b min(-1) and 39.2 degrees C (+/-0.1). The mean sweat rate during exercise for sites within the hairline was 1.95 mg cm(-2) min(-1). However, the evolution of this secretion pattern was not uniformly distributed within the head, with the average sweat rate for the top of the head being significantly lower than at the anterior lateral aspect of the head (P < 0.05), and representing only 30% of the forehead sweat rate (P < 0.05). It is hypothesised that these intra-segmental observations may reflect variations in the local adaptation of eccrine glands to differences in local evaporation associated either with bipedal locomotion, which will influence forehead sweating, or the hidromeiotic suppression of sweating, which impacts upon sweat glands within the hairline.     

Yawning and thermoregulation

We review a growing body of medical and physiological evidence indicating that yawning may be a thermoregulatory mechanism, providing compensatory cooling when other provisions fail to operate favorably. Conditions such as multiple sclerosis, migraine headaches, epilepsy, stress and anxiety, and schizophrenia have all be linked to thermoregulatory dysfunction and are often associated with instances of atypical yawning. Excessive yawning appears to be symptomatic of conditions that increase brain and/or core temperature, such as central nervous system damage, sleep deprivation and specific serotonin reuptake inhibitors. Yawning is also associated with drowsiness, and subjective ratings of sleepiness are correlated with increases in body temperature. This view of yawning has widespread application for the basic physiological understanding of thermoregulation as well as for the improved diagnosis and treatment of diseases associated with abnormal thermoregulation.     

桂枝汤对发热及低体温大鼠下丘脑15-羟基前列腺素脱氢酶活性的影响

目的：研究桂枝汤对发热和低体温大鼠下丘脑组织内15-PGDH活性的影响，进一步阐明桂枝汤体温双向调节作用机制。方法：采用核素示踪技术测定酵母性发热和安痛定性低体温大鼠及桂枝汤处理组下丘脑组织内15-PGDH活性，并观察其与体温变化的关系。结果：皮下注射酵母可降低下丘脑15-PGDH活性，桂枝汤灌胃可剂量依赖性地抑制该变化并促进发热大鼠体温的恢复，两者呈正相关；而腹腔注射安痛定后，随着体温下降，15-PGDH活性有升高倾向，桂枝汤可抑制该酶活性并加速体温恢复正常，但两者呈弱相关。结论：大鼠下丘脑内15-PGDH可能参与机体体温调节并可能是桂枝汤解热作用靶点之一，但与其抗低体温作用关联不大。